The invention relates to an apparatus for heating a sheet- or web-like material during its passage through a processing machine, provided with at least one heating panel which faces the path of travel of the material and is equipped with a number of infrared-radiation producing elements that are energized from a source of alternating current.
Such apparatuses are used in various fields, such as, for instance, for sheetfed and rotary machines, so as to attain an improvement in the quality and processability of the material processed, as well as a higher processing rate. However, the prior-art systems of this kind have the disadvantage that the heating panel is equipped with infrared elements having a relatively great thermal inertia, while the operation of the heating panel is controlled merely by on-and-off switching of the infrared elements.
Accordingly, the heating panel of the prior-art apparatus must be energized some time before the processing machine is started, so that the sheet- or web-like material may at once be heated to the required degree. These prior-art systems furthermore necessitate relatively complicated mechanical constructions in order to prevent, when the material comes to a standstill, the heat produced by the heating panel, and released by it even after it has been switched off, from reaching the sheet- or web-like material, since this material could ignite under its action. The prior-art systems moreover have the disadvantage that, because of the absence of a control of the heat supplied by the panel during operation, a variation of the rate of travel of the material results in a corresponding variation in the temperature of the material, thus causing the quality of the end product to be negatively affected.